/* Copyright (c) 2020 XEPIC Corporation Limited */
/*
 * Copyright (c) 2002-2010 Stephen Williams (steve@icarus.com)
 *
 *    This source code is free software; you can redistribute it
 *    and/or modify it in source code form under the terms of the GNU
 *    General Public License as published by the Free Software
 *    Foundation; either version 2 of the License, or (at your option)
 *    any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 * USA.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "globals.h"
#include "ivl_alloc.h"

char* substitutions(const char* str) {
  size_t nbuf = strlen(str) + 1;
  char* buf = malloc(nbuf);
  char* cp = buf;

  while (*str) {
    if ((str[0] == '$') && ((str[1] == '(') || str[1] == '{')) {
      /* If I find a $(x) or ${x} string in the source, replace
         it in the destination with the contents of the
         environment variable x. */
      char* name;
      char* value;
      const char* ep = strchr(str, (str[1] == '(') ? ')' : '}');
      str += 2;

      name = malloc(ep - str + 1);
      strncpy(name, str, ep - str);
      name[ep - str] = 0;

      str = ep + 1;

      value = getenv(name);
      if (value == 0) {
        fprintf(stderr,
                "Warning: environment variable "
                "\"%s\" not found during command file "
                "processing.\n",
                name);
        free(name);
        continue;
      }
      free(name);

      if (strlen(value) >= (nbuf - (cp - buf))) {
        size_t old_size = cp - buf;
        nbuf = (cp - buf) + strlen(value) + 1;
        buf = realloc(buf, nbuf);
        cp = buf + old_size;
      }

      strcpy(cp, value);
      cp += strlen(cp);

    } else {
      if (cp == (buf + nbuf)) {
        size_t old_size = nbuf;
        nbuf = old_size + 32;
        buf = realloc(buf, nbuf);
        cp = buf + old_size;
      }

      *cp++ = *str++;
    }
  }

  /* Add the trailing nul to the string, and reallocate the
     buffer to be a tight fit. */
  if (cp == (buf + nbuf)) {
    size_t old_size = nbuf;
    nbuf = old_size + 1;
    buf = realloc(buf, nbuf);
    buf[old_size] = 0;
  } else {
    *cp++ = 0;
    nbuf = cp - buf;
    buf = realloc(buf, nbuf);
  }

  return buf;
}
